The present invention relates to an absorption cooling apparatus that is used as an outdoor machine for an absorption air conditioning system and which cools the heat transfer medium used to activate the cooling operation of an indoor air conditioner.
Among the known absorption cooling apparatuses is the one that is described in the Unexamined Japanese Patent Application Publication No. Hei 10-26437 and which is applied to an absorption air conditioning system. This absorption cooling apparatus uses water as a refrigerant and lithium bromide as an absorbent. The general layout of the cooling apparatus is shown in FIG. 8 and comprises the following components: a high-temperature generator having a fin-and-tube heat exchanger 112 which uses the heat of combustion from a burner 111 to heat an aqueous solution of lithium bromide (which is hereunder referred to simply as either a low-concentration solution, a medium-concentration solution or a high-concentration solution depending upon the concentration of lithium bromide), or a low-concentration absorbing liquid supplied from a solution pump 150; a gas-liquid separator 113 for high-temperature generator (which is hereunder referred to simply as a high-temperature separator) with which the low-concentration solution heated with the high-temperature generator 110 is separated into steam and a medium-concentration solution; a low-temperature generator 120 with which the medium-concentration solution being sent to a fin-and-tube heat exchanger 121 is heated with the steam separated in the high-temperature separator 113; a gas-liquid separator 122 for low-temperature generator (which is hereunder referred to simply as a low-temperature separator) with which the heated medium-concentration solution is separated into steam and a high-concentration solution; a condenser 130 which cools the steam from the low-temperature separator 122 to liquefy; an evaporator 141 which evaporates the water condensed in the condenser 130 and the low-temperature generator 120; and an absorber 142 that allows the steam from the evaporator 141 to be absorbed by the high-concentration solution.
The evaporator 141 and the absorber 142 have a dual pipe structure consisting of a cold water pipe 160 extending from an indoor cooler (not shown) surrounded with a coaxial outer pipe 140 and they are formed integrally with an evaporating/absorbing compartment 143 formed between the cold water pipe 160 and the outer pipe 140. The absorber 142 is connected to the high-temperature generator 110 via a solution circulating path K on which are provided the following three components: the solution pump 150 which supplies in circulation a low-concentration solution to the high-temperature generator 110; a low-temperature heat exchanger 151 which performs heat exchange with the high-concentration solution being sent from the low-temperature separator 122; and a high-temperature heat exchanger 152 which performs heat exchange with the medium-concentration solution being sent from the high-temperature separator 113. A pressure reducing valve 114 is provided on the solution circulating path extending from the high-temperature heat exchanger 152 to the low-temperature generator 120.
This absorption cooling apparatus operates as follows in a cooling mode. The solution pump 150 starts to operate and the burner 111 ignites, whereupon the low-concentration solution flowing through the fin-and-tube heat exchanger in the high-temperature generator 110 is heated to generate steam, which is separated from the medium-concentration solution in the high-temperature separator 113. The medium-concentration solution has the temperature thereof lowered in the high-temperature heat exchanger 152 and is thereafter supplied into the low-temperature generator 120. As it flows through the fin-and-tube heat exchanger in the low-temperature generator 120, the medium-concentration solution is reheated by the steam from the high-temperature separator 113 and enters the low-temperature separator 122, where it is separated into steam and the high-concentration solution. The high-concentration solution has the temperature thereof lowered in the low-temperature heat exchanger 151 and is thereafter dripped on the inner surface of the outer pipe 140. The steam is cooled to condense in the condenser 130 and dripped on the outer surface of the cold water pipe 160 in the evaporating/absorbing compartment 143. The dripping water evaporates under the low pressure in the evaporating/absorbing compartment 143 and cools the water flowing through the cold water pipe 160 by depriving it of the heat equivalent to the heat of vaporization; the resulting cold water circulates through the cold water pipe 160 and is directed to the indoor cooler to perform a cooling operation. The high-concentration solution absorbs the water vapor (steam) to become a low-concentration solution which is forced by the solution pump 150 to pass through the low-temperature heat exchanger 151 and the high-temperature heat exchanger 152, so that the temperature thereof is raised; thereafter, the low-concentration solution is sent to the high-temperature generator 110.
The above-described absorption cooling apparatus has various problems. If a pressure reducing means such as an orifice is not provided between the high-temperature separator 113 and the low-temperature generator 120, the pressure difference between the two components will increase during normal operation of the cooling apparatus and steam flows into the high-temperature heat exchanger 152, making it impossible to perform appropriate heat exchange, thus upsetting the balance in the refrigeration cycle to interfere with the appropriate operation. Another problem is that if the pressure reducing means such as an orifice is the only element that is provided between the high-temperature separator 113 and the low-temperature generator 120, the head of the high-temperature separator 113 is not sufficient to assure the appropriate flow of the solution during a diluting operation, a start-up period or other stages where only small pressure difference exists between the two components. The same difficulty occurs between the low-temperature separator 122 and the low-temperature heat exchanger 151. A further problem arises with the low-temperature separator 122: due to the high concentration of the solution formed therein, lithium bromide tends to crystallize out if the solution stays for a long period. The reducing pressure valve 114 provided in the conventional absorption cooling apparatus is not capable of accommodating the variations in pressure difference.